I believe that this is a limitation imposed by the method of connection to
the data source.  In Word, click on the Pizza Button and then on Customize
in the bottom border of the dialog and then click on the Advance item and
scroll down to the General section and check the box against the "Confirm
file format conversion at open" item.  Then when you connect to the data
source you will be presented with a dialog in which you can specifiy the
method of connection.  Try the DDE option.

Unless something has chnaged in the SP1 release of Office 2007, none of the
available methods lets you see more than 255 columns. When I tested here,
the DDE method was actually worse than it has been in previous versions.
When I raised the issue, the problem was described as a "Product
Limitation", which I think means that no-one is ever going to attempt to
overcome it, but I'm not completely sure about that.

If that is still true, your only option is to export to a delimited text
file and see if Word can connect to that Word has a converter that may still
be able to read more than 255 columns. /But/ Word can also have difficulties
connecting to such data sources.